As such system having the battery and the power load, as disclosed, for instance, in Patent Document 1, it is a battery warming-up system having a battery of an electric vehicle and a heater that controls a temperature of the battery by warming up the battery when the battery is unused.
It is conceivable that the battery mounted in the electric vehicle is used in a cold district, and a battery electrolyte might freeze while the battery is unused.
When the temperature of the battery lowers, although a battery charge state SOC does not lower, a usable input/output power for the battery decreases due to an increase of an internal resistance. Further, when the battery electrolyte freezes, the usable input/output power of the battery finally becomes 0 (zero), then in a case of the electric vehicle that uses the battery as a travelling energy source, the electric vehicle gets into a travel-impossible state.
Thus, a battery temperature control device, which controls the battery temperature by warming up the battery by the heater before the battery temperature lowers to a temperature that causes a state in which such problem of the usable input/output power of the battery occurs, is required.
The battery warming-up system disclosed in Patent Document 1, for example when controlling the battery temperature by warming up the battery by the heater for such sake, performs the control as follows.
That is, when the battery temperature lowers below a predetermined temperature, the battery warming-up system warms up the battery by operating the heater. However, at the same time as this warming-up, if the battery charge state is less than a predetermined value, the battery warming-up system further performs charge of the battery, and the battery is warmed up also by heat generated by this battery charge.
In the case of a technique disclosed in Patent Document 1, however, when the battery temperature lowers below the predetermined temperature, if the battery charge state is less than the predetermined value, the battery charge is also performed. Because of this, at this time, as long as the battery temperature is lower than the predetermined temperature, the battery is continuously charged until the battery charge state is equal to or greater than the predetermined value.
Here, regarding the charge of the battery, it is preferable to charge the battery using low-priced midnight power (late-night off-peak electricity) from the viewpoint of reduction of a running cost. For instance, in order to respond to such request, or in order that the battery is in a fully charged state at a departure time, it is desirable that a time of the battery charge can be designated or nominated.
In a case where the battery warming-up system of Patent Document 1 is applied to the vehicle in which the time of the battery charge can be designated, the following problems arise.
That is, as described above, since the battery warming-up system of Patent Document 1 is a system that, when the battery temperature lowers below the predetermined temperature and also the battery charge state is less than the predetermined value, charges the battery so as to increase the battery charge state, the battery charge for increasing the battery charge state is carried out at a time except the above battery charge designated time.
When the battery charge for increasing the battery charge state is carried out at the time except the battery charge designated time, for instance, such problems that the battery charge using the low-priced midnight power is not performed and at least relatively great proportion of a charging amount of the battery is covered by high-priced power other than the midnight power then the running cost increases arise.